Characterizing Porous Absorption in Recycled Packaging Paper Grades
Characterizing porous absorption in recycled paper requires measuring dynamic capillary wicking and pore size distribution to control ink set times and glue bonds.
Starch Adhesive Gelling
Phase Conversion
Thermal energy input forces uncooked starch granules suspended in water to swell, absorb liquid, and transform into a viscous adhesive gel. Heating occurs inside corrugating machine double facer units where heat transfers from hot plates into paperboard flutes. Initiating starch adhesive gelling bonds corrugated medium flutes securely to outer linerboard sheets under pressure.
Raw starch granules rupture at specific gelatinization temperatures, releasing amylose and amylopectin polymer chains. Viscosity rises sharply as starch polymer networks trap surrounding water molecules.
Viscosity Transition
Rapid swelling of raw starch solids converts fluid carrier suspensions into high viscosity gel structures within milliseconds. Temperature control across heating plates dictates the exact speed of adhesive bond formation. Incomplete starch adhesive gelling produces weak bond strength, resulting in corrugating sheet delamination during box conversion.
Caustic soda additions lower gelatinization temperature requirements, tailoring adhesive performance to press speeds. Gel formation creates strong green bond strength prior to final moisture evaporation in drying sections. Rheological measurements track viscosity jumps across gelatinization temperature ranges.
Gelation Threshold
Gel formation begins precisely when starch slurry temperatures reach the gelatinization point. Complete polymer hydration marks the end of viscosity growth inside the glue line. Mechanical bonding completes as water evaporates from the gel structure.